using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace POSV.Utils
{
    public class HashUtils
    {
        // BKDR Hash Function
        public static int Hash1(string str)
        {
            int seed = 131; // 31 131 1313 13131 131313 etc..
            int hash = 0;
            int count;
            char[] bitarray = str.ToCharArray();
            count = bitarray.Length;
            while (count > 0)
            {
                hash = hash * seed + (bitarray[bitarray.Length - count]);
                count--;
            }

            return (hash & 0x7FFFFFFF);
        }
        //AP hash function
        public static int Hash2(string str)
        {
            int hash = 0;
            int i;
            int count;
            char[] bitarray = str.ToCharArray();
            count = bitarray.Length;
            for (i = 0; i < count; i++)
            {
                if ((i & 1) == 0)
                {
                    hash ^= ((hash << 7) ^ (bitarray[i]) ^ (hash >> 3));
                }
                else
                {
                    hash ^= (~((hash << 11) ^ (bitarray[i]) ^ (hash >> 5)));
                }
                count--;
            }

            return (hash & 0x7FFFFFFF);
        }

        //SDBM Hash function
        public static int Hash3(string str)
        {
            int hash = 0;
            int i;
            int count;
            char[] bitarray = str.ToCharArray();
            count = bitarray.Length;

            while (count > 0)
            {
                // equivalent to: hash = 65599*hash + (*str++);
                hash = (bitarray[bitarray.Length - count]) + (hash << 6) + (hash << 16) - hash;
                count--;
            }

            return (hash & 0x7FFFFFFF);
        }

        // RS Hash Function
        public static int Hash4(string str)
        {
            int b = 378551;
            int a = 63689;
            int hash = 0;

            int i;
            int count;
            char[] bitarray = str.ToCharArray();
            count = bitarray.Length;
            while (count > 0)
            {
                hash = hash * a + (bitarray[bitarray.Length - count]);
                a *= b;
                count--;
            }

            return (hash & 0x7FFFFFFF);
        }

        // JS Hash Function
        public static int Hash5(string str)
        {
            int hash = 1315423911;
            int count;
            char[] bitarray = str.ToCharArray();
            count = bitarray.Length;
            while (count > 0)
            {
                hash ^= ((hash << 5) + (bitarray[bitarray.Length - count]) + (hash >> 2));
                count--;
            }

            return (hash & 0x7FFFFFFF);
        }

        // P. J. Weinberger Hash Function
        public static int Hash6(string str)
        {
            int BitsInUnignedInt = (int)(sizeof(int) * 8);
            int ThreeQuarters = (int)((BitsInUnignedInt * 3) / 4);
            int OneEighth = (int)(BitsInUnignedInt / 8);
            int hash = 0;
            unchecked
            {
                int HighBits = (int)(0xFFFFFFFF) << (BitsInUnignedInt - OneEighth);
                int test = 0;
                int count;
                char[] bitarray = str.ToCharArray();
                count = bitarray.Length;
                while (count > 0)
                {
                    hash = (hash << OneEighth) + (bitarray[bitarray.Length - count]);
                    if ((test = hash & HighBits) != 0)
                    {
                        hash = ((hash ^ (test >> ThreeQuarters)) & (~HighBits));
                    }
                    count--;
                }
            }
            return (hash & 0x7FFFFFFF);
        }

        // ELF Hash Function
        public static int Hash7(string str)
        {
            int hash = 0;
            int x = 0;
            int i;
            int count;
            char[] bitarray = str.ToCharArray();
            count = bitarray.Length;
            unchecked
            {
                while (count > 0)
                {
                    hash = (hash << 4) + (bitarray[bitarray.Length - count]);
                    if ((x = hash & (int)0xF0000000) != 0)
                    {
                        hash ^= (x >> 24);
                        hash &= ~x;
                    }
                    count--;
                }
            }
            return (hash & 0x7FFFFFFF);
        }



        // DJB Hash Function
        public static int Hash8(string str)
        {
            int hash = 5381;
            int i;
            int count;
            char[] bitarray = str.ToCharArray();
            count = bitarray.Length;
            while (count > 0)
            {
                hash += (hash << 5) + (bitarray[bitarray.Length - count]);
                count--;
            }

            return (hash & 0x7FFFFFFF);
        }

    }
}